The inset explains how the grace note is integral with the first proper note (grace note F, to E). The whole phrase of 4 notes has a slur mark, so it's a slur within a phrase, if you like.If that's how the composer wanted it played, can't understand why it wasn't written like that. Dash is interesting.
– TimDec 16 '18 at 8:05

I think @atanii is right about the dashes, but I can tell you more about what the editorial note in the right hand’s first measure means:

When composers of Mozart’s time wanted to write out a group of four running notes that starts on a strong beat, they sometimes needed to prepare (or write) the notes differently than we would today. They would double the length of the second note, and prepare the first note as a grace note tied into the group.

I believe this is due to species counterpoint rules. It used to be considered undesirable to put a dissonant harmonic interval such as the perfect fourth between C and F on a “strong” beat. To circumvent this rule, Classical Era composers would place the second note, in this case a consonant major third, on the strong beat.

But you don’t need to know that to perform this accurately. Play it just as the editorial inlay says: four slurred sixteenth notes, in time.